The present invention relates to thrusters, particularly Hall-effect thrusters, and more particularly to Hall-effect thrusters employing a condensable propellant. Existing thrusters include anodes that are used to supply a gaseous propellant (e.g., xenon) to the plasma discharge of the thruster. The mass flow rate of the gaseous propellant is controlled upstream of the anode by a dedicated control system. Such thrusters are typically mid-power thrusters operating in the 1-kW regime, with a specific impulse of approximately 1500 sec, an efficiency of approximately 50%, approximately 50 mN of thrust, and used mainly in north-south-stationkeeping (NSSK) of geostationary communications satellites. High-power thrusters (e.g., operating at power levels greater than 30 kW) are being developed to extend electric propulsion systems to more diverse applications. Scaling existing mid-power thrusters to larger powers is physically straightforward but is impeded by financial considerations, partly due to low efficiencies.
Condensable metal propellants have recently been found to have performance improvements over gaseous propellants, such as xenon. Existing thrusters employing a metal propellant (e.g., lithium) and a metal vapor supply anode distribute gaseous metal vapors that are created upstream of the anode in a separate boiling tank. As a result, the existing metal vapor supply anodes must be maintained at a temperature higher than the metal boiling temperature to prevent condensation of the metal propellant within the anode, which usually requires the use of auxiliary electric power to heat the solid propellant. Significant power losses and low efficiencies occur as heat radiates from the anode as a result of maintaining the anode at such high temperatures. Therefore, a thruster that minimizes power losses due to heating of the anode and improves control of the evaporation rate of the propellant is desirable.